Controller for optically-switchable windows

ABSTRACT

This disclosure provides a window controller that includes a command-voltage generator that generates a command voltage signal, and a pulse-width-modulated-signal generator that generates a pulse-width-modulated signal based on the command voltage signal. The pulse-width-modulated signal drives an optically-switchable device. The pulse-width-modulated signal comprises a first power component having a first duty cycle and a second power component having a second duty cycle. The first component delivers a first pulse during each active portion of the first duty cycle, and the second component delivers a second pulse during each active portion of the second duty cycle. The first pulses are applied to a first conductive layer and the second pulses are applied to a second conductive layer. The relative durations of the active portions and the relative durations of the first and second pulses are adjusted to result in a change in an effective DC voltage applied across the optically-switchable device.

CROSS REFERENCE TO RELATED APPLICATIONS

The application is related to: U.S. patent application Ser. No.13/049,756 (Attorney Docket No. SLDMP007) naming Brown et al. asinventors, titled MULTIPURPOSE CONTROLLER FOR MULTISTATE WINDOWS andfiled 16 Mar. 2011; U.S. patent application Ser. No. ______ (AttorneyDocket No. SLDMP035) naming Brown as inventor, titled CONTROLLINGTRANSITIONS IN OPTICALLY SWITCHABLE DEVICES and filed 17 Apr. 2012; andU.S. patent application Ser. No. ______ (Attorney Docket No. SLDMP042)naming Brown as inventor, titled CONTROLLER FOR OPTICALLY SWITCHABLEWINDOWS and filed 17 Apr. 2012; all of which are incorporated herein byreference in their entireties and for all purposes.

TECHNICAL FIELD

This disclosure relates generally to optically-switchable devicesincluding electrochromic windows, and more particularly to controllersfor controlling and driving optically-switchable devices.

DESCRIPTION OF THE RELATED TECHNOLOGY

Optically-switchable devices can be integrated with windows to enablecontrol over, for example, the tinting, transmittance, or reflectance ofwindow panes. Optically-switchable devices include electrochromicdevices. Electrochromism is a phenomenon in which a material exhibits areversible electrochemically-mediated change in one or more opticalproperties when stimulated to a different electronic state. For example,the electrochromic material can be stimulated by an applied voltage.Optical properties that can be reversibly manipulated include, forexample, color, transmittance, absorbance, and reflectance. One wellknown electrochromic material is tungsten oxide (WO₃). Tungsten oxide isa cathodic electrochromic material that undergoes a colorationtransition—transparent to blue—by electrochemical action viaintercalation of positive ions into the tungsten oxide matrix withconcurrent charge balance by electron insertion.

Electrochromic materials and the devices made from them may beincorporated into, for example, windows for home, commercial, or otheruses. The color, transmittance, absorbance, or reflectance of suchelectrochromic windows can be changed by inducing a change in theelectrochromic material. For example, electrochromic windows can bedarkened or lightened in response to electrical stimulation. Forexample, a first voltage applied to an electrochromic device of thewindow may cause the window to darken while a second voltage may causethe window to lighten. This capability can allow for control over theintensities of various wavelengths of light that may pass through thewindow, including both the light that passes from an outside environmentthrough the window into an inside environment as well as potentially thelight that passes from an inside environment through the window out toan outside environment.

Such capabilities of electrochromic windows present enormousopportunities for increasing energy efficiency, as well as for aestheticpurposes. With energy conservation being foremost in the minds of manymodern energy policy-makers, it is expected that the growth of theelectrochromic window industry will be robust. An importantconsideration in the engineering of electrochromic windows is how bestto integrate them into new as well as existing (e.g., retrofit)applications. Of particular importance is how best to organize, control,and deliver power to the electrochromic windows.

SUMMARY

According to one innovative aspect, a window controller includes acommand-voltage generator configured to generate a command voltagesignal. The window controller also includes apulse-width-modulated-signal generator configured to generate apulse-width-modulated signal based on the command voltage signal. Thepulse-width-modulated signal is configured to drive anoptically-switchable device on a substantially transparent substrate. Insome embodiments, the pulse-width-modulated signal comprises a firstpower component having a first duty cycle and a second power componenthaving a second duty cycle. In some embodiments, the first powercomponent is configured to deliver a first pulse during each activeportion of the first duty cycle, and the second power component isconfigured to deliver a second pulse during each active portion of thesecond duty cycle. In some embodiments, during operation, the firstpulses are applied to a first conductive electrode layer of theoptically-switchable device and the second pulses are applied to asecond conductive electrode layer of the optically-switchable device. Insome embodiments, the relative durations of the active portions of thefirst and second duty cycles and the relative durations of the first andsecond pulses are adjusted to result in a change in an effective DCvoltage applied across the optically-switchable device.

In some embodiments, the substantially transparent substrate isconfigured in an IGU. In some embodiments, the window controller islocated at least partially within a seal of the IGU. In someembodiments, the optically-switchable device is an electrochromic deviceformed on a surface of the substantially transparent substrate andadjacent an interior volume of the IGU.

In some embodiments, the first duty cycle has a first time period and afirst voltage magnitude, the second duty cycle has a second time periodand a second voltage magnitude, the first time period equals the secondtime period, and the first voltage magnitude equals the second voltagemagnitude. In some embodiments, the window controller also includesfirst and second inductors that couple the first and second powercomponents to the optically-switchable device, the voltage appliedacross the optically-switchable device resulting from the applied firstand second power components is effectively a DC voltage. In someembodiments, the active portion of the first duty cycle comprises afirst fraction of the first time period, the active portion of thesecond duty cycle comprises a second fraction of the second time period,the magnitude of the voltage applied to a first conductive layer of theoptically-switchable device is substantially proportional to the productof the first fraction and the first voltage magnitude, the magnitude ofthe voltage applied to a second conductive layer of theoptically-switchable device is substantially proportional to the productof the second fraction and the second voltage magnitude, and theeffective DC voltage applied across the optically-switchable device issubstantially equal to the difference between the magnitude of thevoltage applied to the first conductive layer and the magnitude of thevoltage applied to the second conductive layer.

In some embodiments, the command-voltage generator includes amicrocontroller configured to generate the command voltage signal. Insome embodiments, the microcontroller generates the command voltagesignal based at least in part on a voltage feedback signal that isitself based on an effective DC voltage applied across theoptically-switchable device. In some embodiments, the microcontrollergenerates the command voltage signal based at least in part on a currentfeedback signal that is itself based on a detected current transmittedthrough the optically-switchable device.

In some embodiments, the window controller also includes a memory deviceconfigured to store one or more drive parameters. In some embodiments,the drive parameters include one or more of a current outsidetemperature, a current inside temperature, a current transmissivityvalue of the electrochromic device, a target transmissivity value of theelectrochromic device, and a transition rate. In some embodiments, themicrocontroller is further configured to modify the command voltagesignal based on one or more other input, feedback, or control signals.The window controller of claim 15, wherein the microcontroller modifiesthe command voltage signal based at least in part on a voltage feedbacksignal that is itself based on a detected actual level of the effectiveDC voltage applied across the optically-switchable device.

According to another innovative aspect, a system includes: a pluralityof windows, each window including an optically-switchable device on asubstantially transparent substrate; a plurality of window controllerssuch as those just described; and a network controller configured tocontrol the plurality of window controllers. In some embodiments, eachwindow controller is configured to generate a command voltage signalbased at least in part and at least at certain times on an inputreceived from the network controller.

In some embodiments, the network controller is configured to communicatewith a building management system and the microcontroller of each windowcontroller is configured to modify the command voltage signal based oninput from the building management system. In some embodiments, thenetwork controller is configured to communicate with one or morelighting systems, heating systems, cooling systems, ventilation systems,power systems, and/or security systems and the microcontroller of eachwindow controller is configured to modify the command voltage signalbased on input from the one or more lighting systems, heating systems,cooling systems, ventilation systems, power systems, and/or securitysystems.

Details of one or more embodiments or implementations of the subjectmatter described in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages will become apparent from the description, the drawings, andthe claims. Note that the relative dimensions of the following figuresmay not be drawn to scale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a depiction of a system for controlling and driving aplurality of electrochromic windows.

FIG. 2 shows a cross-sectional axonometric view of an exampleelectrochromic window that includes two window panes.

FIG. 3 shows an example of a voltage profile for driving an opticalstate transition in an electrochromic device.

FIG. 4 shows a depiction of an example plug-in component including awindow controller.

FIG. 5A shows a depiction of an example transistor implementation of apulse-width modulator circuit.

FIG. 5B shows a depiction of an equivalent H-bridge configurationrepresentation of the pulse-width modulator circuit of FIG. 5A.

FIG. 5C shows voltage profiles for the configurations of FIGS. 5A and5B.

FIG. 6 shows an example 3-dimensional data structure including driveparameters for driving an electrochromic device.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following detailed description is directed to certain embodiments orimplementations for the purposes of describing the innovative aspects.However, the teachings herein can be applied and implemented in amultitude of different ways. Furthermore, while the disclosedembodiments focus on electrochromic windows (also referred to as smartwindows), the concepts disclosed herein may apply to other types ofswitchable optical devices including, for example, liquid crystaldevices and suspended particle devices, among others. For example, aliquid crystal device or a suspended particle device, rather than anelectrochromic device, could be incorporated into some or all of thedisclosed embodiments.

Referring to FIG. 1 as an example, some embodiments relate to a system,100, for controlling and driving (e.g., selectively powering) aplurality of electrochromic windows, 102. System 100, adapted for use ina building, 104, is used for controlling and driving a plurality ofexterior facing electrochromic windows 102. Some embodiments findparticularly advantageous use in buildings such as commercial officebuildings or residential buildings. Some embodiments can be particularlysuited and adapted for use in the construction of new buildings. Forexample, some embodiments of system 100 are designed to work inconjunction with modern or novel heating, ventilation, and airconditioning (HVAC) systems, 106, interior lighting systems, 107,security systems, 108, and power systems, 109, as a single holisticefficient energy control system for the entire building 104, or campusof buildings 104. Some embodiments are particularly well-suited forintegration with a building management system (BMS), 110. A BMS is acomputer-based control system that can be installed in a building tomonitor and control the building's mechanical and electrical equipmentsuch as HVAC systems, lighting systems, power systems, elevators, firesystems, and security systems. A BMS consists of hardware and associatedfirmware or software for maintaining conditions in the buildingaccording to preferences set by the occupants or a building manager orother administrator. The software can be based on, for example, internetprotocols or open standards.

A BMS is typically used in large buildings, and typically functions atleast to control the environment within the building. For example, a BMSmay control lighting, temperature, carbon dioxide levels, and humiditywithin a building. Typically, there are many mechanical or electricaldevices that are controlled by a BMS such as, for example, heaters, airconditioners, blowers, and vents. To control the building environment, aBMS may turn on and off these various devices according to pre-definedrules or in response to pre-defined conditions. A core function of atypical modern BMS is to maintain a comfortable environment for thebuilding's occupants while minimizing heating and cooling energy lossesand costs. A modern BMS can be used not only to monitor and control, butalso to optimize the synergy between various systems, for example, toconserve energy and lower building operation costs.

Some embodiments are alternatively or additionally designed to workresponsively or reactively based on feedback sensed through, forexample, thermal, optical, or other sensors or through input from, forexample, an HVAC or interior lighting system, or an input from a usercontrol. Some embodiments also can be utilized in existing structures,including both commercial and residential structures, having traditionalor conventional HVAC or interior lighting systems. Some embodiments alsocan be retrofitted for use in older residential homes.

In some embodiments, system 100 includes a network controller, 112. Insome embodiments, network controller 112 controls a plurality of windowcontrollers, 114. For example, network controller 112 can control tens,hundreds, or even thousands of window controllers 114. Each windowcontroller 114, in turn, can control and drive one or moreelectrochromic windows 102. The number and size of the electrochromicwindows 102 that each window controller 114 can drive is generallylimited by the voltage and current characteristics of the load on thewindow controller 114 controlling the respective electrochromic windows102. In some embodiments, the maximum window size that each windowcontroller 114 can drive is limited by the voltage, current, or powerrequirements to cause the desired optical transitions in theelectrochromic window 102 within a desired time-frame. Such requirementsare, in turn, a function of the surface area of the window. In someembodiments, this relationship is nonlinear. For example, the voltage,current, or power requirements can increase nonlinearly with the surfacearea of the electrochromic window 102. For example, in some cases therelationship is nonlinear at least in part because the sheet resistanceof the first and second conductive layers 230 and 238 (see FIG. 2)increases nonlinearly with distance across the length and width of thefirst or second conductive layers. In some embodiments, the relationshipbetween the voltage, current, or power requirements required to drivemultiple electrochromic windows 102 of equal size and shape is, however,directly proportional to the number of the electrochromic windows 102being driven.

In the following description, each electrochromic window 102 will bereferred to as an insulated glass unit (IGU) 102. This convention isassumed, for example, because it is common and can be desirable to haveIGUs serve as the fundamental construct for holding an electrochromiclite or pane. Additionally, IGUs, especially those having double ortriple pane window configurations, offer superior thermal insulationover single pane configurations. However, this convention is forconvenience only because, as described below, in many implementationsthe basic unit of an electrochromic window can be considered to includea pane or substrate of transparent material, upon which anelectrochromic coating or device is deposited, and to which associatedelectrical connections are coupled to power the electrochromic coatingor device.

FIG. 2 shows a cross-sectional axonometric view of an embodiment of anIGU 102 that includes two window panes, 216. In various embodiments,each IGU 102 can include one, two, or more substantially transparent(e.g., at no applied voltage) window panes 216 as well as a frame, 218,that supports the panes 216. For example, the IGU 102 shown in FIG. 2 isconfigured as a double-pane window. One or more of the panes 216 canitself be a laminate structure of two, three, or more layers or panes(e.g., shatter-resistant glass similar to automotive windshield glass).In each IGU 102, at least one of the panes 216 includes anelectrochromic device or stack, 220, disposed on at least one of itsinner surface, 222, or outer surface, 224: for example, the innersurface 222 of the outer pane 216.

In multi-pane configurations, each adjacent set of panes 216 can have avolume, 226, disposed between them. Generally, each of the panes 216 andthe IGU 102 as a whole are rectangular and form a rectangular solid.However, in other embodiments other shapes (e.g., circular, elliptical,triangular, curvilinear, convex, concave) may be desired. In someembodiments, the volume 226 between the panes 116 is evacuated of air.In some embodiments, the IGU 102 is hermetically-sealed. Additionally,the volume 226 can be filled (to an appropriate pressure) with one ormore gases, such as argon (Ar), krypton (Kr), or xenon (Xn), forexample. Filling the volume 226 with a gas such as Ar, Kr, or Xn canreduce conductive heat transfer through the IGU 102 because of the lowthermal conductivity of these gases. The latter two gases also canimpart improved acoustic insulation due to their increased weight.

In some embodiments, frame 218 is constructed of one or more pieces. Forexample, frame 218 can be constructed of one or more materials such asvinyl, PVC, aluminum (Al), steel, or fiberglass. The frame 218 may alsoinclude or hold one or more foam or other material pieces that work inconjunction with frame 218 to separate the window panes 216 and tohermetically seal the volume 226 between the panes 216. For example, ina typical IGU implementation, a spacer lies between adjacent panes 216and forms a hermetic seal with the panes in conjunction with an adhesivesealant that can be deposited between them. This is termed the primaryseal, around which can be fabricated a secondary seal, typically of anadditional adhesive sealant. In some such embodiments, frame 218 can bea separate structure that supports the IGU construct.

Each pane 216 includes a substantially transparent or translucentsubstrate, 228. Generally, substrate 228 has a first (e.g., inner)surface 222 and a second (e.g., outer) surface 224 opposite the firstsurface 222. In some embodiments, substrate 228 can be a glasssubstrate. For example, substrate 228 can be a conventional siliconoxide (SO_(x))-based glass substrate such as soda-lime glass or floatglass, composed of, for example, approximately 75% silica (SiO₂) plusNa₂O, CaO, and several minor additives. However, any material havingsuitable optical, electrical, thermal, and mechanical properties may beused as substrate 228. Such substrates also can include, for example,other glass materials, plastics and thermoplastics (e.g., poly(methylmethacrylate), polystyrene, polycarbonate, allyl diglycol carbonate, SAN(styrene acrylonitrile copolymer), poly(4-methyl-1-pentene), polyester,polyamide), or mirror materials. If the substrate is formed from, forexample, glass, then substrate 228 can be strengthened, e.g., bytempering, heating, or chemically strengthening. In otherimplementations, the substrate 228 is not further strengthened, e.g.,the substrate is untempered.

In some embodiments, substrate 228 is a glass pane sized for residentialor commercial window applications. The size of such a glass pane canvary widely depending on the specific needs of the residence orcommercial enterprise. In some embodiments, substrate 228 can be formedof architectural glass. Architectural glass is typically used incommercial buildings, but also can be used in residential buildings, andtypically, though not necessarily, separates an indoor environment froman outdoor environment. In certain embodiments, a suitable architecturalglass substrate can be at least approximately 20 inches by approximately20 inches, and can be much larger, for example, approximately 80 inchesby approximately 120 inches, or larger. Architectural glass is typicallyat least about 2 millimeters (mm) thick and may be as thick as 6 mm ormore. Of course, electrochromic devices 220 can be scalable tosubstrates 228 smaller or larger than architectural glass, including inany or all of the respective length, width, or thickness dimensions. Insome embodiments, substrate 228 has a thickness in the range ofapproximately 1 mm to approximately 10 mm.

Electrochromic device 220 is disposed over, for example, the innersurface 222 of substrate 228 of the outer pane 216 (the pane adjacentthe outside environment). In some other embodiments, such as in coolerclimates or applications in which the IGUs 102 receive greater amountsof direct sunlight (e.g., perpendicular to the surface of electrochromicdevice 220), it may be advantageous for electrochromic device 220 to bedisposed over, for example, the inner surface (the surface bordering thevolume 226) of the inner pane adjacent the interior environment. In someembodiments, electrochromic device 220 includes a first conductive layer(CL) 230, an electrochromic layer (EC) 232, an ion conducting layer (IC)234, a counter electrode layer (CE) 236, and a second conductive layer(CL) 238. Again, layers 230, 232, 234, 236, and 238 are alsocollectively referred to as electrochromic stack 220. A power source 240operable to apply an electric potential across a thickness ofelectrochromic stack 220 effects the transition of the electrochromicdevice 220 from, for example, a bleached or lighter state (e.g., atransparent, semitransparent, or translucent state) to a colored ordarker state (e.g., a tinted, less transparent or less translucentstate). In some other embodiments, the order of layers 230, 232, 234,236, and 238 can be reversed or otherwise reordered or rearranged withrespect to substrate 238.

In some embodiments, one or both of first conductive layer 230 andsecond conductive layer 238 is formed from an inorganic and solidmaterial. For example, first conductive layer 230, as well as secondconductive layer 238, can be made from a number of different materials,including conductive oxides, thin metallic coatings, conductive metalnitrides, and composite conductors, among other suitable materials. Insome embodiments, conductive layers 230 and 238 are substantiallytransparent at least in the range of wavelengths where electrochromismis exhibited by the electrochromic layer 232. Transparent conductiveoxides include metal oxides and metal oxides doped with one or moremetals. For example, metal oxides and doped metal oxides suitable foruse as first or second conductive layers 230 and 238 can include indiumoxide, indium tin oxide (ITO), doped indium oxide, tin oxide, doped tinoxide, zinc oxide, aluminum zinc oxide, doped zinc oxide, rutheniumoxide, doped ruthenium oxide, among others. First and second conductivelayers 230 and 238 also can be referred to as “transparent conductiveoxide” (TCO) layers.

In some embodiments, commercially available substrates, such as glasssubstrates, already contain a transparent conductive layer coating whenpurchased. In some embodiments, such a product can be used for bothsubstrate 238 and conductive layer 230 collectively. Examples of suchglass substrates include conductive layer-coated glasses sold under thetrademark TEC Glass™ by Pilkington, of Toledo, Ohio and SUNGATE™ 300 andSUNGATE™ 500 by PPG Industries of Pittsburgh, Pa. Specifically, TECGlass™ is, for example, a glass coated with a fluorinated tin oxideconductive layer.

In some embodiments, first or second conductive layers 230 and 238 caneach be deposited by physical vapor deposition processes including, forexample, sputtering. In some embodiments, first and second conductivelayers 230 and 238 can each have a thickness in the range ofapproximately 0.01 μm to approximately 1 μm. In some embodiments, it maybe generally desirable for the thicknesses of the first and secondconductive layers 230 and 238 as well as the thicknesses of any or allof the other layers described below to be individually uniform withrespect to the given layer; that is, that the thickness of a given layeris uniform and the surfaces of the layer are smooth and substantiallyfree of defects or other ion traps.

A primary function of the first and second conductive layers 230 and 238is to spread an electric potential provided by a power source 240, suchas a voltage or current source, over surfaces of the electrochromicstack 220 from outer surface regions of the stack to inner surfaceregions of the stack, with relatively little Ohmic potential drop fromthe outer regions to the inner regions (e.g., as a result of a sheetresistance of the first and second conductive layers 230 and 238). Inother words, it can be desirable to create conductive layers 230 and 238that are each capable of behaving as substantially equipotential layersacross all portions of the respective conductive layer along the lengthand width of the electrochromic device 220. In some embodiments, busbars 242 and 244, one (e.g., bus bar 242) in contact with conductivelayer 230 and one (e.g., bus bar 244) in contact with conductive layer238 provide electric connection between the voltage or current source240 and the conductive layers 230 and 238. For example, bus bar 242 canbe electrically coupled with a first (e.g., positive) terminal 246 ofpower source 240 while bus bar 244 can be electrically coupled with asecond (e.g., negative) terminal 248 of power source 240.

In some embodiments, IGU 102 includes a plug-in component 250. In someembodiments, plug-in component 250 includes a first electrical input 252(e.g., a pin, socket, or other electrical connector or conductor) thatis electrically coupled with power source terminal 246 via, for example,one or more wires or other electrical connections, components, ordevices. Similarly, plug-in component 250 can include a secondelectrical input 254 that is electrically coupled with power sourceterminal 248 via, for example, one or more wires or other electricalconnections, components, or devices. In some embodiments, firstelectrical input 252 can be electrically coupled with bus bar 242, andfrom there with first conductive layer 230, while second electricalinput 254 can be coupled with bus bar 244, and from there with secondconductive layer 238. The conductive layers 230 and 238 also can beconnected to power source 240 with other conventional means as well asaccording to other means described below with respect to windowcontroller 114. For example, as described below with reference to FIG.4, first electrical input 252 can be connected to a first power linewhile second electrical input 254 can be connected to a second powerline. Additionally, in some embodiments, third electrical input 256 canbe coupled to a device, system, or building ground. Furthermore, in someembodiments, fourth and fifth electrical inputs/outputs 258 and 260,respectively, can be used for communication between, for example, windowcontroller 114, or microcontroller 274, and network controller 112, asdescribed below.

In some embodiments, electrochromic layer 232 is deposited or otherwiseformed over first conductive layer 230. In some embodiments,electrochromic layer 232 is formed of an inorganic and solid material.In various embodiments, electrochromic layer 232 can include or beformed of one or more of a number of electrochromic materials, includingelectrochemically cathodic or electrochemically anodic materials. Forexample, metal oxides suitable for use as electrochromic layer 232 caninclude tungsten oxide (WO₃), molybdenum oxide (MoO₃), niobium oxide(Nb₂O₅), titanium oxide (TiO₂), copper oxide (CuO), iridium oxide(Ir₂O₃), chromium oxide (Cr₂O₃), manganese oxide (Mn₂O₃), vanadium oxide(V₂O₅), nickel oxide (Ni₂O₃), and cobalt oxide (Co₂O₃), among othermaterials. In some embodiments, electrochromic layer 232 can have athickness in the range of approximately 0.05 μm to approximately 1 μm.

During operation, in response to a voltage generated across thethickness of electrochromic layer 232 by first and second conductivelayers 230 and 238, electrochromic layer 232 transfers or exchanges ionsto or from counter electrode layer 236 resulting in the desired opticaltransitions in electrochromic layer 232, and in some embodiments, alsoresulting in an optical transition in counter electrode layer 236. Insome embodiments, the choice of appropriate electrochromic and counterelectrode materials governs the relevant optical transitions.

In some embodiments, counter electrode layer 236 is formed of aninorganic and solid material. Counter electrode layer 236 can generallyinclude one or more of a number of materials or material layers that canserve as a reservoir of ions when the electrochromic device 220 is in,for example, the transparent state. For example, suitable materials forthe counter electrode layer 236 include nickel oxide (NiO), nickeltungsten oxide (NiWO), nickel vanadium oxide, nickel chromium oxide,nickel aluminum oxide, nickel manganese oxide, nickel magnesium oxide,chromium oxide (Cr₂O₃), manganese oxide (MnO₂), and Prussian blue. Insome embodiments, counter electrode layer 236 can have a thickness inthe range of approximately 0.05 82 m to approximately 1 μm. In someembodiments, counter electrode layer 236 is a second electrochromiclayer of opposite polarity as electrochromic layer 232. For example,when electrochromic layer 232 is formed from an electrochemicallycathodic material, counter electrode layer 236 can be formed of anelectrochemically anodic material.

During an electrochromic transition initiated by, for example,application of an appropriate electric potential across a thickness ofelectrochromic stack 220, counter electrode layer 236 transfers all or aportion of the ions it holds to electrochromic layer 232, causing theoptical transition in the electrochromic layer 232. In some embodiments,as for example in the case of a counter electrode layer 236 formed fromNiWO, the counter electrode layer 236 also optically transitions withthe loss of ions it has transferred to the electrochromic layer 232.When charge is removed from a counter electrode layer 236 made of NiWO(e.g., ions are transported from the counter electrode layer 236 to theelectrochromic layer 232), the counter electrode layer 236 willtransition in the opposite direction (e.g., from a transparent state toa darkened state).

In some embodiments, ion conducting layer 234 serves as a medium throughwhich ions are transported (e.g., in the manner of an electrolyte) whenthe electrochromic device 220 transitions between optical states. Insome embodiments, ion conducting layer 234 is highly conductive to therelevant ions for the electrochromic and the counter electrode layers232 and 236, but also has sufficiently low electron conductivity suchthat negligible electron transfer occurs during normal operation. A thinion conducting layer 234 with high ionic conductivity permits fast ionconduction and hence fast switching for high performance electrochromicdevices 220. In some embodiments, ion conducting layer 234 can have athickness in the range of approximately 0.01 μm to approximately 1 μm.

In some embodiments, ion conducting layer 234 also is inorganic andsolid. For example, ion conducting layer 234 can be formed from one ormore silicates, silicon oxides, tungsten oxides, tantalum oxides,niobium oxides, and borates. The silicon oxides includesilicon-aluminum-oxide. These materials also can be doped with differentdopants, including lithium. Lithium-doped silicon oxides include lithiumsilicon-aluminum-oxide.

In some other embodiments, the electrochromic and the counter electrodelayers 232 and 236 are formed immediately adjacent one another,sometimes in direct contact, without separately depositing an ionconducting layer. For example, in some embodiments, electrochromicdevices having an interfacial region between first and second conductiveelectrode layers rather than a distinct ion conducting layer 234 can beutilized. Such devices, and methods of fabricating them, are describedin U.S. patent application Ser. Nos. 12/772,055 and 12/772,075, eachfiled 30 Apr. 2010, and in U.S. patent application Ser. Nos. 12/814,277and 12/814,279, each filed 11 Jun. 2010, all four of which are titledELECTROCHROMIC DEVICES and name Zhongchun Wang et al. as inventors. Eachof these four applications is incorporated by reference herein in itsentirety.

In some embodiments, electrochromic device 220 also can include one ormore additional layers (not shown), such as one or more passive layers.For example, passive layers used to improve certain optical propertiescan be included in or on electrochromic device 220. Passive layers forproviding moisture or scratch resistance also can be included inelectrochromic device 220. For example, the conductive layers 230 and238 can be treated with anti-reflective or protective oxide or nitridelayers. Other passive layers can serve to hermetically seal theelectrochromic device 220.

Additionally, in some embodiments, one or more of the layers inelectrochromic stack 220 can contain some amount of organic material.Additionally or alternatively, in some embodiments, one or more of thelayers in electrochromic stack 220 can contain some amount of liquids inone or more layers. Additionally or alternatively, in some embodiments,solid state material can be deposited or otherwise formed by processesemploying liquid components such as certain processes employing sol-gelsor chemical vapor deposition.

Additionally, transitions between a bleached or transparent state and acolored or opaque state are but one example, among many, of an opticalor electrochromic transition that can be implemented. Unless otherwisespecified herein (including the foregoing discussion), wheneverreference is made to a bleached-to-opaque transition (or to and fromintermediate states in between), the corresponding device or processdescribed encompasses other optical state transitions such as, forexample, intermediate state transitions such as percent transmission (%T) to % T transitions, non-reflective to reflective transitions (or toand from intermediate states in between), bleached to coloredtransitions (or to and from intermediate states in between), and colorto color transitions (or to and from intermediate states in between).Further, the term “bleached” may refer to an optically neutral state,for example, uncolored, transparent or translucent. Still further,unless specified otherwise herein, the “color” of an electrochromictransition is not limited to any particular wavelength or range ofwavelengths.

Generally, the colorization or other optical transition of theelectrochromic material in electrochromic layer 232 is caused byreversible ion insertion into the material (for example, intercalation)and a corresponding injection of charge-balancing electrons. Typically,some fraction of the ions responsible for the optical transition isirreversibly bound up in the electrochromic material. Some or all of theirreversibly bound ions can be used to compensate “blind charge” in thematerial. In some embodiments, suitable ions include lithium ions (Li+)and hydrogen ions (H+) (i.e., protons). In some other embodiments,however, other ions can be suitable. Intercalation of lithium ions, forexample, into tungsten oxide (WO_(3-y)(0<y≦˜0.3)) causes the tungstenoxide to change from a transparent (e.g., bleached) state to a blue(e.g., colored) state.

In particular embodiments described herein, the electrochromic device220 reversibly cycles between a transparent state and an opaque ortinted state. In some embodiments, when the device is in a transparentstate, a potential is applied to the electrochromic stack 220 such thatavailable ions in the stack reside primarily in the counter electrodelayer 236. When the magnitude of the potential on the electrochromicstack 220 is reduced or its polarity reversed, ions are transported backacross the ion conducting layer 234 to the electrochromic layer 232causing the electrochromic material to transition to an opaque, tinted,or darker state. In certain embodiments, layers 232 and 236 arecomplementary coloring layers; that is, for example, when ions aretransferred into the counter electrode layer it is not colored.Similarly, when or after the ions are transferred out of theelectrochromic layer it is also not colored. But when the polarity isswitched, or the potential reduced, however, and the ions aretransferred from the counter electrode layer into the electrochromiclayer, both the counter electrode and the electrochromic layers becomecolored.

In some other embodiments, when the device is in an opaque state, apotential is applied to the electrochromic stack 220 such that availableions in the stack reside primarily in the counter electrode layer 236.In such embodiments, when the magnitude of the potential on theelectrochromic stack 220 is reduced or its polarity reversed, ions aretransported back across the ion conducting layer 234 to theelectrochromic layer 232 causing the electrochromic material totransition to a transparent or lighter state. These layers may also becomplementary coloring.

FIG. 3 shows an example of a voltage profile for driving an opticalstate transition in an electrochromic device (e.g., electrochromicdevice 220). The magnitude of the DC voltages (e.g., supplied by powersource 240) applied to an electrochromic device 220 may depend in parton the thickness of the electrochromic stack and the size (e.g., surfacearea) of the electrochromic device 220. A voltage profile 300 caninclude the following sequence of applied voltage or current parametersfor driving electrochromic device 220 from a first state to a coloredstate, and from a colored state to a bleached state: a negative ramp301, a negative hold 303, a positive ramp 305, a negative hold 307, apositive ramp 309, a positive hold 311, a negative ramp 313, and apositive hold 315. In some embodiments, the voltage remains constantduring the length of time that the device remains in its defined opticalstate, e.g., in negative hold 307 or positive hold 315. Negative ramp301 drives the device to the colored or opaque state (or an intermediatepartially transparent state) and negative hold 307 maintains the devicein the transitioned-to state for a desired period of time. In someembodiments, negative hold 303 may be applied for a specified durationof time or until another condition is met, such as a desired amount ofionic charge being passed sufficient to cause the desired change incoloration, for example. Positive ramp 305, increases the voltage fromthe maximum magnitude negative voltage (e.g., negative hold 303) to thesmaller magnitude negative voltage (e.g., negative hold 307) used tohold the desired optical state. By performing a first negative ramp 301(and a first negative hold voltage 303 at this peak negative voltage) to“overdrive” electrochromic device 220, the inertia of the ions isovercome more rapidly and the desired target optical state is reachedsooner. The second negative hold voltage 307 effectively serves tocounteract the voltage drop that would otherwise result from the leakagecurrent. As the leakage current is reduced for any given electrochromicdevice 220, the hold voltage required to hold the desired opticaltransition can approach zero.

In some embodiments, positive ramp 309 drives the transition of theelectrochromic device from the colored or opaque state (or anintermediate less transparent state) to the bleached or transparentstate (or an intermediate more transparent state). Positive hold 315maintains the device in the transitioned-to state for a desired periodof time. In some embodiments, positive hold 311 may be applied for aspecified duration of time or until another condition is met, such as adesired amount of ionic charge being passed sufficient to cause thedesired change in coloration, for example. Negative ramp 313, decreasesthe voltage from the maximum magnitude positive voltage (e.g., positivehold 311) to the smaller magnitude positive voltage (e.g., positive hold315) used to hold the desired optical state. By performing a firstpositive ramp 309 (and a first positive hold voltage 311 at this peakpositive voltage) to “overdrive” electrochromic device 220, the inertiaof the ions is overcome more rapidly and the desired target opticalstate is reached sooner. The second positive hold voltage 315effectively serves to counteract the voltage drop that would otherwiseresult from the leakage current. As the leakage current is reduced forany given electrochromic device 220, the hold voltage required to holdthe desired optical transition can approach zero.

The rate of the optical transition can be a function of not only theapplied voltage, but also the temperature and the voltage ramping rate.For example, since both voltage and temperature affect lithium iondiffusion, the amount of charge passed (and hence the intensity of theionic current peak) increases with voltage and temperature.Additionally, because voltage and temperature are interdependent, thisimplies that a lower voltage can be used at higher temperatures toattain the same transition rate as a higher voltage at lowertemperatures. This temperature response can be exploited in avoltage-based switching algorithm as described below. The temperature isused to determine which voltage to apply in order to effect rapidtransitioning without damaging the device.

In some embodiments, electrical input 252 and electrical input 254receive, carry, or transmit complementary power signals. In someembodiments, electrical input 252 and its complement electrical input254 can be directly connected to the bus bars 242 and 244, respectively,and on the other side, to an external power source that provides avariable DC voltage (e.g., sign and magnitude). The external powersource can be window controller 114 itself, or power from building 104transmitted to window controller 114 or otherwise coupled to electricalinputs 252 and 254. In such an embodiment, the electrical signalstransmitted through electrical inputs/outputs 258 and 260 can bedirectly connected to memory device 292, described below, to allowcommunication between window controller 114 and memory device 292.Furthermore, in such an embodiment, the electrical signal input toelectrical input 256 can be internally connected or coupled (within IGU102) to either electrical input 252 or 254 or to the bus bars 242 or 244in such a way as to enable the electrical potential of one or more ofthose elements to be remotely measured (sensed). This can allow windowcontroller 114 to compensate for a voltage drop on the connecting wiresfrom the window controller 114 to the electrochromic device 220.

In some embodiments, the window controller 114 can be immediatelyattached (e.g., external to the IGU 102 but inseparable by the user) orintegrated within the IGU 102. For example, U.S. patent application Ser.No. 13/049,750 (Attorney Docket No. SLDMP008) naming Brown et al. asinventors, titled ONBOARD CONTROLLER FOR MULTISTATE WINDOWS and filed 16Mar. 2011, incorporated by reference herein, describes in detail variousembodiments of an “onboard” controller. In such an embodiment,electrical input 252 can be connected to the positive output of anexternal DC power source. Similarly, electrical input 254 can beconnected to the negative output of the DC power source. As describedbelow, however, electrical inputs 252 and 254 can, alternately, beconnected to the outputs of an external low voltage AC power source(e.g., a typical 24 V AC transformer common to the HVAC industry). Insuch an embodiment, electrical inputs/outputs 258 and 260 can beconnected to the communication bus between window controller 114 and thenetwork controller 112 as described below. In this embodiment,electrical input/output 256 can be eventually (e.g., at the powersource) connected with the earth ground (e.g., Protective Earth, or PEin Europe) terminal of the system.

As just described, although the voltages plotted in FIG. 3 are expressedas DC voltages, in some embodiments, the voltages actually supplied bythe external power source are AC voltage signals, In some otherembodiments, the supplied voltage signals are converted to pulse-widthmodulated voltage signals. However, as described below with reference toFIG. 4, the voltages actually “seen” or applied to the bus bars 242 and244 are effectively DC voltages. The frequency of the oscillations ofthe applied voltage signal can depend on various factors including theleakage current of the electrochromic device 220, the sheet resistanceof the conductive layers 230 and 238, the desired end or target state(e.g., % T), or a critical length of a part (e.g., the distance betweenbus bars 242 and 244). Typically, the voltage oscillations applied atterminals 246 and 248 are in the range of approximately 1 Hz to 1 MHz,and in particular embodiments, approximately 100 kHz. The amplitude ofthe oscillations also can depend on numerous factors including thedesired level of the desired intermediate target state. However, in someexample applications, the amplitude of the applied voltage oscillationscan be in the range of approximately 0 volts (V) to 24 V while, asdescribed below, the amplitude of the DC voltage actually applied to busbars 240 and 242 can be in the range of approximately 0.01 V and 10 V,and in some applications, in the range of approximately 0.5 V and 3 V.In various embodiments, the oscillations have asymmetric residence timesfor the darkening (e.g., tinting) and lightening (e.g., bleaching)portions of a period. For example, in some embodiments, transitioningfrom a first less transparent state to a second more transparent staterequires more time than the reverse; that is, transitioning from themore transparent second state to the less transparent first state. Aswill be described below, a controller can be designed or configured toapply a driving voltage meeting these requirements.

The oscillatory applied voltage control allows the electrochromic device220 to operate in, and transition to and from, one or more intermediatestates without any necessary modification to the electrochromic devicestack 220 or to the transitioning time. Rather, window controller 114can be configured or designed to provide an oscillating drive voltage ofappropriate wave profile, taking into account such factors as frequency,duty cycle, mean voltage, amplitude, among other possible suitable orappropriate factors. Additionally, such a level of control permits thetransitioning to any intermediate state over the full range of opticalstates between the two end states. For example, an appropriatelyconfigured controller can provide a continuous range of transmissivity(% T) which can be tuned to any value between end states (e.g., opaqueand bleached end states).

To drive the device to an intermediate state using the oscillatorydriving voltage, as described above, a controller could simply apply theappropriate intermediate voltage. However, there are more efficient waysto reach the intermediate optical state. This is partly because highdriving voltages can be applied to reach the end states but aretraditionally not applied to reach an intermediate state. One techniquefor increasing the rate at which the electrochromic device 220 reaches adesired intermediate state is to first apply a high voltage pulsesuitable for full transition (to an end state) and then back off to thevoltage of the oscillating intermediate state (just described). Statedanother way, an initial low frequency single pulse (low in comparison tothe frequency employed to maintain the intermediate state) of magnitudeand duration chosen for the intended final state can be employed tospeed the transition. After this initial pulse, a higher frequencyvoltage oscillation can be employed to sustain the intermediate statefor as long as desired.

As described above, in some particular embodiments, each IGU 102includes a plug-in component 250 that in some embodiments is “pluggable”or readily-removable from IGU 102 (e.g., for ease of maintenance,manufacture, or replacement). In some particular embodiments, eachplug-in component 250 itself includes a window controller 114. That is,in some such embodiments, each electrochromic device 220 is controlledby its own respective local window controller 114 located within plug-incomponent 250. In some other embodiments, window controller 114 isintegrated with another portion of frame 218, between the glass panes inthe secondary seal area, or within volume 226. In some otherembodiments, window controller 114 can be located external to IGU 102.In various embodiments, each window controller 114 can communicate withthe IGUs 102 it controls and drives, as well as communicate to otherwindow controllers 114, network controller 112, BMS 110, or otherservers, systems, or devices (e.g., sensors), via one or more wired(e.g., Ethernet) networks or wireless (e.g., WiFi) networks, forexample, via wired (e.g., Ethernet) interface 263 or wireless (WiFi)interface 265. Embodiments having Ethernet or Wifi capabilities are alsowell-suited for use in residential homes and other smaller-scalenon-commercial applications. Additionally, the communication can bedirect or indirect, e.g., via an intermediate node between a mastercontroller such as network controller 112 and the IGU 102.

FIG. 4 shows a depiction of an example plug-in component 250 including awindow controller 114. In some embodiments, window controller 114communicates with network controller 112 over a communication bus 262.For example, communication bus 262 can be designed according to theController Area Network (CAN) vehicle bus standard. In such embodiments,first electrical input 252 can be connected to a first power line 264while second electrical input 254 can be connected to a second powerline 266. In some embodiments, as described above, the power signalssent over power lines 264 and 266 are complementary; that is,collectively they represent a differential signal (e.g., a differentialvoltage signal). In some embodiments, line 268 is coupled to a system orbuilding ground (e.g., an Earth Ground). In such embodiments,communication over CAN bus 262 (e.g., between microcontroller 274 andnetwork controller 112) may proceed along first and second communicationlines 270 and 272 transmitted through electrical inputs/outputs 258 and260, respectively, according to the CANopen communication protocol orother suitable open, proprietary, or overlying communication protocol.In some embodiments, the communication signals sent over communicationlines 270 and 272 are complementary; that is, collectively theyrepresent a differential signal (e.g., a differential voltage signal).

In some embodiments, plug-in component 250 couples CAN communication bus262 into window controller 114, and in particular embodiments, intomicrocontroller 274. In some such embodiments, microcontroller 274 isalso configured to implement the CANopen communication protocol.Microcontroller 274 is also designed or configured (e.g., programmed) toimplement one or more drive control algorithms in conjunction withpulse-width modulated amplifier or pulse-width modulator (PWM) 276,smart logic 278, and signal conditioner 280. In some embodiments,microcontroller 274 is configured to generate a command signalV_(COMMAND), e.g., in the form of a voltage signal, that is thentransmitted to PWM 276. PWM 276, in turn, generates a pulse-widthmodulated power signal, including first (e.g., positive) componentV_(PW1) and second (e.g., negative) component V_(PW2), based onV_(COMMAND). Power signals V_(PW1) and V_(PW2) are then transmittedover, for example, interface 288, to IGU 102, or more particularly, tobus bars 242 and 244 in order to cause the desired optical transitionsin electrochromic device 220. In some embodiments, PWM 276 is configuredto modify the duty cycle of the pulse-width modulated signals such thatthe durations of the pulses in signals V_(PW1) and V_(PW2) are notequal: for example, PWM 276 pulses V_(PW1) with a first 60% duty cycleand pulses V_(PW2) for a second 40% duty cycle. The duration of thefirst duty cycle and the duration of the second duty cycle collectivelyrepresent the duration, t_(PWM) of each power cycle. In someembodiments, PWM 276 can additionally or alternatively modify themagnitudes of the signal pulses V_(PW1) and V_(PW2).

In some embodiments, microcontroller 274 is configured to generateV_(COMMAND) based on one or more factors or signals such as, forexample, any of the signals received over CAN bus 262 as well as voltageor current feedback signals, V_(FB) and I_(FB) respectively, generatedby PWM 276. In some embodiments, microcontroller 274 determines currentor voltage levels in the electrochromic device 220 based on feedbacksignals I_(FB) or V_(FB), respectively, and adjusts V_(COMMAND)according to one or more rules or algorithms to effect a change in therelative pulse durations (e.g., the relative durations of the first andsecond duty cycles) or amplitudes of power signals V_(PW1) and V_(PW2)to produce the voltage profiles described above with respect to FIG. 3.Additionally or alternatively, microcontroller 274 can also adjustV_(COMMAND) in response to signals received from smart logic 278 orsignal conditioner 280. For example, a conditioning signal V_(CON) canbe generated by signal conditioner 280 in response to feedback from oneor more networked or non-networked devices or sensors, such as, forexample, an exterior photosensor or photodetector 282, an interiorphotosensor or photodetector 284, a thermal or temperature sensor 286,or a tint command signal V_(TC). For example, additional embodiments ofsignal conditioner 280 and V_(CON) are also described in U.S. patentapplication Ser. No. ______ (Attorney Docket No. SLDMP035) naming Brownas inventor, titled CONTROLLING TRANSITIONS IN OPTICALLY SWITCHABLEDEVICES and filed 17 Apr. 2012.

Referring back, V_(TC) can be an analog voltage signal between 0 V and10 V that can be used or adjusted by users (such as residents orworkers) to dynamically adjust the tint of an IGU 102 (for example, auser can use a control in a room or zone of building 104 similarly to athermostat to finely adjust or modify a tint of the IGUs 102 in the roomor zone) thereby introducing a dynamic user input into the logic withinmicrocontroller 274 that determines V_(COMMAND). For example, when setin the 0 to 2.5 V range, V_(TC) can be used to cause a transition to a5% T state, while when set in the 2.51 to 5 V range, V_(TC) can be usedto cause a transition to a 20% T state, and similarly for other rangessuch as 5.1 to 7.5 V and 7.51 to 10 V, among other range and voltageexamples. In some embodiments, signal conditioner 280 receives theaforementioned signals or other signals over a communication bus orinterface 290. In some embodiments, PWM 276 also generates V_(COMMAND)based on a signal V_(SMART) received from smart logic 278, as describedbelow. In some embodiments, smart logic 278 transmits V_(SMART) over acommunication bus such as, for example, an Inter-Integrated Circuit(I²C) multi-master serial single-ended computer bus. In some otherembodiments, smart logic 278 communicates with memory device 292 over a1-WIRE device communications bus system protocol (by DallasSemiconductor Corp., of Dallas, Tex.).

In some embodiments, microcontroller 274 includes a processor, chip,card, or board, or a combination of these, which includes logic forperforming one or more control functions. Power and communicationfunctions of microcontroller 274 may be combined in a single chip, forexample, a programmable logic device (PLD) chip or field programmablegate array (FPGA), or similar logic. Such integrated circuits cancombine logic, control and power functions in a single programmablechip. In one embodiment, where one pane 216 has two electrochromicdevices 220 (e.g., on opposite surfaces) or where IGU 102 includes twoor more panes 216 that each include an electrochromic device 220, thelogic can be configured to control each of the two electrochromicdevices 220 independently from the other. However, in one embodiment,the function of each of the two electrochromic devices 220 is controlledin a synergistic fashion, for example, such that each device iscontrolled in order to complement the other. For example, the desiredlevel of light transmission, thermal insulative effect, or otherproperty can be controlled via a combination of states for each of theindividual electrochromic devices 220. For example, one electrochromicdevice may be placed in a colored state while the other is used forresistive heating, for example, via a transparent electrode of thedevice. In another example, the optical states of the two electrochromicdevices are controlled so that the combined transmissivity is a desiredoutcome.

As described above, in some embodiments, microcontroller 274, or windowcontroller 114 generally, also can have wireless capabilities, such aswireless control and powering capabilities. For example, wirelesscontrol signals, such as radio-frequency (RF) signals or infra-red (IR)signals can be used, as well as wireless communication protocols such asWiFi (mentioned above), Bluetooth, Zigbee, EnOcean, among others, tosend instructions to the microcontroller 274 and for microcontroller 274to send data out to, for example, other window controllers 114, networkcontroller 112, or directly to BMS 110. In various embodiments, wirelesscommunication can be used for at least one of programming or operatingthe electrochromic device 220, collecting data or receiving input fromthe electrochromic device 220 or the IGU 102 generally, collecting dataor receiving input from sensors, as well as using the window controller114 as a relay point for other wireless communications. Data collectedfrom IGU 102 also can include count data, such as a number of times anelectrochromic device 220 has been activated (cycled), an efficiency ofthe electrochromic device 220 over time, among other useful data orperformance metrics.

Window controller 114 also can have wireless power capability. Forexample, window controller 114 can have one or more wireless powerreceivers that receive transmissions from one or more wireless powertransmitters as well as one or more wireless power transmitters thattransmit power transmissions enabling window controller 114 to receivepower wirelessly and to distribute power wirelessly to electrochromicdevice 220. Wireless power transmission includes, for example,induction, resonance induction, RF power transfer, microwave powertransfer, and laser power transfer. For example, U.S. patent applicationSer. No. 12/971,576 (Attorney Docket No. SLDMP003) naming Rozbicki asinventor, titled WIRELESS POWERED ELECTROCHROMIC WINDOWS and filed 17Dec. 2010, incorporated by reference herein, describes in detail variousembodiments of wireless power capabilities.

In order to achieve a desired optical transition, the pulse-widthmodulated power signal is generated such that the positive componentV_(PW1) is supplied to, for example, bus bar 244 during the firstportion of the power cycle, while the negative component V_(PW2) issupplied to, for example, bus bar 242 during the second portion of thepower cycle. As described above, the signals V_(PW1) and V_(PW2) areeffectively DC signals as seen by electrochromic device 220 as a resultof, for example, the inductance of series inductors 312 and 314 (seeFIGS. 5A and 5B) within PWM 276, or of various other components ofwindow controller 114 or electrochromic device 220 in relation to thefrequency of the pulse-width modulated power signals V_(PW1) andV_(PW2). More specifically, referring now to FIG. 5C, the inductance issuch that the inductors 312 and 314 effectively filter out the highestfrequency components in the voltages V_(TEC) and V_(ITO), the voltagesapplied to the first and second conductive layers 230 and 238,respectively, and thus the effective voltage V_(EFF) applied across thebus bars 242 and 244 is effectively constant when the first and secondduty cycles are constant.

In some cases, depending on the frequency (or inversely the duration) ofthe pulse-width modulated signals, this can result in bus bar 244floating at substantially the fraction of the magnitude of V_(PW1) thatis given by the ratio of the duration of the first duty cycle to thetotal duration t_(PWM) of the power cycle. Similarly, this can result inbus bar 242 floating at substantially the fraction of the magnitude ofV_(PW2) that is given by the ratio of the duration of the second dutycycle to the total duration t_(PWM) of the power cycle. In this way, insome embodiments, the difference between the magnitudes of thepulse-width modulated signal components V_(PW1) and V_(PW2) is twice theeffective DC voltage across terminals 246 and 248, and consequently,across electrochromic device 220. Said another way, in some embodiments,the difference between the fraction (determined by the relative durationof the first duty cycle) of V_(PW1) applied to bus bar 244 and thefraction (determined by the relative duration of the second duty cycle)of V_(PW2) applied to bus bar 242 is the effective DC voltage V_(EFF)applied to electrochromic device 220. The current IEFF through theload—electromagnetic device 220—is roughly equal to the effectivevoltage VEFF divided by the effective resistance (represented byresistor 316) or impedance of the load.

In some embodiments, the relative durations of the first and second dutycycles—the durations of the V_(PW1) and V_(PW2) pulses, respectively—arebased on V_(COMMAND). In some embodiments, in order to generate the twoopposing polarity signals V_(PW1) and V_(PW2), PWM 276, and IGU 102generally, is designed according to an H-bridge configuration 294. Insome embodiments, PWM 276 is constructed using four transistors 296,298, 300, and 302 powered by a supply voltage V_(SUPPLY) as shown inFIG. 5A. Transistors 296, 298, 300, and 302 can be, for example,metal-oxide-semiconductor field-effect transistors (MOSFETs). In someimplementations, transistors 296 and 300 are n-type MOSFET transistorswhile transistors 298 and 302 are p-type MOSFET transistors. In someimplementations, during a first portion of operation, the gate oftransistor 296 receives signal A, while the gate of transistor 302receives its complement Ā such that when signal A is high Ā is low, andthus, transistors 296 and 302 are conducting while transistors 298 and300 are not. In this configuration, current from V_(SUPPLY) istransferred through transistor 296, through the load, includingelectromagnetic device 220, through transistor 302 and ultimately toground. This results in a power signal pulse V_(PW1) during this portionof operation. Similarly, in some implementations, during a secondportion of operation, the gate of transistor 300 receives signal B,while the gate of transistor 298 receives the complement of signal B,and thus, transistors 300 and 298 are conducting while transistors 296and 302 are not. In this configuration, current from V_(SUPPLY) istransferred through transistor 300, through the load, includingelectromagnetic device 220, through transistor 298 and ultimately toground. This results in a power signal pulse V_(PW2) during this portionof operation.

FIG. 5B shows a depiction of an equivalent H-bridge configurationrepresentation 294 in which switches 304, 306, 308, and 310 representtransistors 296, 298, 300, and 302. Based on V_(COMMAND), H-Bridge 294synchronously transitions from a first state (represented by solidarrows), to generate the first duty cycle (V_(PW1) pulse), to a secondstate (represented by dotted arrows), to generate the second duty cycle(V_(PW2) pulse). For example, in the first state the switches 304 and310 can be closed (e.g., transistors 296 and 302 are conducting) andswitches 306 and 308 can be open (e.g., transistors 298 and 300 are notconducting). Similarly, in the second state switches 306 and 308 can beclosed (e.g., transistors 298 and 300 are conducting) and switches 304and 310 can be open (e.g., transistors 296 and 302 are not conducting).As described above, in some embodiments, the first and second dutycycles of the pulse-width modulated signals V_(PW1) and V_(PW2) are notsymmetric; that is, neither the first nor the second duty cycle is a 50%duty cycle. For example, in the case of a 100 kHz signal, V_(PW1) couldbe pulsed for more than half the time constant t_(PWM) (e.g., more than5 micro-seconds (μs)) followed by V_(PW2) being pulsed for less thanhalf the time constant t_(PWM) (e.g., less than 5 μs), and so onresulting in a first duty cycle of greater than 50% and a second dutycycle of less than 50%. As a result, even when the magnitudes of V_(PW1)and V_(PW2) are equal and remain constant, the effective voltage at theload (e.g., electrochromic device 220) can be changed from the static DCvoltage generated across the load when the duty cycles are symmetric(e.g., (V_(PW1)−V_(PW2))/2). Thus, by varying the duty cycles such thatthey are non-symmetric, a voltage ramp (e.g., ramps 301, 305, 309, or313) can be applied across the electrochromic device 220. It is this DCvoltage that drives the additional ion transfer that causes the opticaltransitions in electrochromic device 220. Additionally, the duty cyclesalso can be varied such that a static DC voltage is developed tocompensate, for example, for ions trapped in defects.

This method—pulse-width modulation—of applying the DC voltage acrosselectrochromic device 220 provides increased protection from damage ascompared to, for example, devices that simply use a battery or other DCvoltage source. DC voltages sources such as batteries can result ininitial current spikes that can permanently damage the electrochromicdevice 220 in the form of, for example, defects that trap ions.Furthermore, by adjusting the relative durations of the pulses V_(PW1)and V_(PW2) of each duty cycle based on the command signal V_(COMMAND),the command signal V_(COMMAND) can be used to change the applied DCvoltage at the electrochromic device 220 (e.g., to produce ramps 301,305, 309, and 313) continuously without changing the magnitude of thesupply voltage V_(SUPPLY).

Additionally, in some embodiments, the transistors 296, 298, 300, and302 (or switches 304, 306, 308, and 310) can be configured at certaintimes to all be insulating (or open) enabling certain embodiments ofelectrochromic device 220 to hold at a desired optical state without anapplied voltage. In some embodiments, this configuration can be used tosave energy by not drawing power from V_(SUPPLY), which is typically themain electrical power for the building 104. In such a configuration, theelectrochromic device 220 could be left floating. In some otherembodiments, in this configuration, the electrochromic device 220 couldreceive power from another source to hold the desired optical state,such as from, for example, a photovoltaic cell on or within the IGU 102.Similarly, in some embodiments, the transistors 296, 298, 300, and 302(or switches 304, 306, 308, and 310) can be configured at certain timesto all be conducting (or closed) and shorted to ground enabling adischarge of electrochromic device 220. In such embodiments,appropriately sized resistors can be arranged within the H-bridgeconfiguration 294 between each transistor or switch and ground to easeor to make more graceful the discharge of the electrochromic device 220.

In some embodiments, microcontroller 274 is programmed to darken orlighten (e.g., change the % T of) the windows on various sides,surfaces, or zones of a building 104 at certain times of day as well asaccording to certain times of year, according to certain conditions orin response to other feedback, or based on manual input. For example,microcontroller 274 can be programmed to darken east-facing IGUs 102 at9:00 am for 1 hour during winter months while at the same timelightening west-facing IGUs. As another example, microcontroller 274 canbe programmed to darken an IGU 102 based on light intensity detectedoutside by a photodetector. In some such embodiments, microcontroller274 can be programmed to continue to darken the IGU 102 as long as lightdetected inside by a second photodetector remains above a thresholdamount of interior light intensity, or until a lighting system 107 ornetwork controller 112 transmits an input command to window controller114 commanding the window controller 114 to stop tinting such that thelighting system can remain off or at a lower energy operational levelwhile enabling workers to have enough ambient light or other light tocontinue working. As another example, microcontroller 274 can beprogrammed to darken an IGU 102 based on a manual input from a user, forexample, in his or her own office relative to a baseline % T commandedby network controller 112.

In some embodiments, the drive or device parameters for a given IGU 102are stored within the IGU 102, in the frame 218, or in an internal orexternal electrical connection assembly wired to the frame or IGU. Inparticular embodiments, the drive and device parameters for the IGU 102are stored within the plug-in component 250. In some particularembodiments, the drive and device parameters are stored withinnon-volatile memory device 292, which may be included within or beexternal to window controller 114 or plug-in component 250, but which,in particular embodiments, is located within IGU 102. In someembodiments, upon inserting and connecting plug-in component 250 intoIGU 102 or upon powering or otherwise activating window controller 114,memory device 292 transfers or loads the drive or device parameters to afast dynamic memory (e.g., a random access memory (RAM), DRAM, NVRAM, orother flash memory) location within microcontroller 274 for quick accessby microcontroller 274. In some embodiments, window controller 114 canperiodically poll for memory device 292, and when window controller 114detects memory device 292, it can transfer the drive parameters to theRAM or other faster memory location within microcontroller 274. In someembodiments, memory device 292 can be a chip (e.g., computer chip havingprocessing or logic capabilities in addition to storing capabilities)designed according to the 1-WIRE device communications bus systemprotocol. In some embodiments, memory device 292 can include solid stateserial memory (e.g. EEPROM (E²PROM), I²C, or SPI), which can also beprogrammable memory.

In some embodiments, the drive parameters can be used by microcontroller274 in conjunction with one or more voltage profiles, currentalgorithms, or voltage and current operating instructions fortransitioning electrochromic device 220 from a first optical state to asecond optical state. In some embodiments, microcontroller 274 uses thedrive parameters to calculate or select a voltage profile (e.g., aportion of voltage profile 300) and, using the voltage profile, togenerate the associated command voltages V_(COMMAND) to achieve thecalculated or selected voltage profile. For example, in someembodiments, a voltage profile can be selected from a number ofpre-determined profiles (e.g., stored or loaded within microcontroller274 or other suitable accessible memory location) based on one or moreof a multitude of drive parameters including, for example, a currenttemperature outside, a current temperature inside, a % T of the first orcurrent optical state, a % T of the second or desired optical state, ora desired transition or ramp (e.g., ramp 301 or 309) rate, as well asvarious initial driving voltages, holding voltages, among otherparameters. Some drive parameters, such as % T and ramp rate, can begenerated prior to manufacture of the device, for example, basedtheoretically or empirically on a number of device parameters including,for example, the size, shape, thickness, age, or number of cyclesexperienced by electrochromic pane 216. In some embodiments, eachvoltage profile can, in turn, be determined theoretically or empiricallyprior to manufacture of the device based on the drive and deviceparameters.

In some embodiments, microcontroller 274 calculates V_(COMMAND) valuesduring operation of IGU 102 based on the selected voltage profile anddrive parameters. In some other embodiments, microcontroller 274 selectsdiscrete V_(COMMAND) values previously calculated and stored based onthe selected voltage profile and drive parameters. However, as describedabove, in some cases V_(COMMAND) can additionally be modified accordingto one or more other input or feedback signals, such as signals V_(CON),V_(FB), or I_(FB), for example, based on input from temperature sensorsor photodetectors, voltage feedback from electrochromic device 220 orPWM 276, or current feedback from electrochromic device 220 or PWM 276.For example, as the outside environment becomes brighter, themicrocontroller 274 can be programmed to darken the electrochromicdevice 220, but as the electrochromic device 220 darkens the temperatureof the device can rise significantly as a result of the increased photonabsorption and, because the tinting of the electrochromic device 220 isdependent on the temperature of the device, the tinting could change ifnot compensated for by, for example, modifying V_(COMMAND) in responseto a signal, such as V_(CON), V_(FB), or I_(FB). Furthermore, in somecases, the voltage profiles themselves stored in the microcontroller 274or memory device 292 can be modified temporarily (e.g., in RAM) orpermanently/perpetually (e.g., in memory device 292) based on signalsreceived from, for example, network controller 112.

In some embodiments, the drive and device parameters stored within agiven IGU 102 can be transmitted, for example via CAN communication bus262, to network controller 112 periodically, in response to certainconditions, or at other appropriate times. Additionally, in someembodiments, drive parameters, voltage profiles, current algorithms,location or zone membership parameters (e.g. at what location or in whatzone of the building 104 is this IGU 102 and controller 114), digitaloutput states, and generally various digital controls (tint, bleach,auto, reboot, etc.) can be transmitted from network controller 112 towindow controller 114 and microcontroller 274 as well as to memorydevice 292 for storage and subsequent use. Network controller 112 alsocan be configured to transmit to microcontroller 274 or memory device292 information relating to a location of the IGU 102 or building 104(e.g., a latitude, longitude, or region parameter), a time of day, or atime of year. Additionally, the drive or device parameters can containinformation specifying a maximum voltage or current level that cansafely be applied to electrochromic device 220 by a window controller114. In some embodiments, network controller 112 can be programmed orconfigured to compare the actual current being output to a particularIGU 102 and electrochromic device 220 to the current expected to beoutput to the IGU 102 based on the device or drive characteristics(e.g., transmitted from the memory device 292 to the microcontroller 274and to the network controller 112), or otherwise determine that they aredifferent or different beyond a threshold range of acceptability, andthereafter signal an alarm, shut off power to the IGU 102, or take someother action to, for example, prevent damage to the electrochromicdevice 220. Furthermore, memory device 292 also can include cycling orother performance data for electrochromic device 220.

In some embodiments, the drive parameters are organized into ann-dimensional data array, structure, or matrix. FIG. 6 shows an example3-dimensional data structure 600 of drive parameters for driving anelectrochromic device 220. Data structure 600 is a 3-by-4-by-4 matrix ofelements 624. A voltage profile is associated with each element 624. Forexample, matrix element (0, 3, 3) is associated with voltage profile 626while matrix element (1, 0, 1) is associated with voltage profile 628.In the illustrated example, each matrix element 624 is specified forthree drive parameters that define the element 624 and thus thecorresponding voltage profile. For example, each matrix element 624 isspecified for a given temperature range value (e.g., <0 degrees Celsius,0-50 degrees Celsius, or >50 degrees Celsius), a current % T value(e.g., 5%, 20%, 40%, or 70%), and a target % T value (e.g., 5%, 20%,40%, or 70%).

In some embodiments, each voltage profile includes one or more specificparameters (e.g., ramp rate, target voltage, and applied voltageduration) or a combination of one or more specific parameters. Forexample, each voltage profile can include one or more specificparameters for each of one or more profile portions or zones (e.g., S1,S2, S3, S4) for making the desired optical transition from the current %T, at a current temperature, to a target % T at the same or a differenttemperature. For example, voltage profile 626 contains parameters totransition a electrochromic window from 70% T to 5% T, at a temperatureless than zero degrees Celsius. To complete this transition, voltageprofile 626 provides an initial ramp S1 (e.g., a rate in mV/s for aspecified time duration or to a specified target voltage value), a firsthold S2 (e.g., specified in V for a specified time duration), a secondramp S3 (e.g., a rate in mV/s for a specified time duration or to aspecified target voltage value), and a fourth hold S4 (e.g., a specifiedholding voltage to maintain the target % T). Similarly, voltage profile628 can provide a different initial ramp S1 (e.g., a flatter voltageramp), a different hold S2 (e.g., a longer hold at this holdingvoltage), a different second ramp S3 (e.g., a shorter but steeper ramp),and a different fourth hold S4 (e.g., the holding voltage to maintainthe target % T) based on the different drive parameters associated withthat element (in this example, transitioning from 20% T to 70% T at atemperature of between zero and fifty degrees Celsius).

Each voltage profile in the n-dimensional data matrix may, in someimplementations, be unique. For example, because even at the sametemperature, transitioning from 70% T to 5% T often cannot be achievedby a simple reversal of the voltage profile used to transition from 5% Tto 70% T, a different voltage profile may be required or at leastdesirable. Put another way, by virtue of the device architecture andmaterials, bleaching is not simply the reverse of coloring; devicesoften behave differently for each transition due to differences indriving forces for ion intercalation and deintercalation to and from theelectrochromic materials.

In other embodiments, the data structure can have another number ofdimensions n, that is, be more or less granular than matrix 600. Forexample, in some embodiments, more drive parameters can be included. Inone embodiment, 288 drive parameters are used including threetemperature range values, four current % T values, and four target % Tvalues resulting in a 3-dimensional matrix having 36 matrix elements and72 corresponding voltage profiles, each of which has one or morespecific parameters (e.g., ramp rate, target voltage, and appliedvoltage duration, or a combination of one or more specific parameters)for each of one or more profile portions or zones (e.g., S1, S2, S3, . .. ). In other embodiments, the number of temperature bins or ranges ofvalues can be increased or decreased (e.g., 5 or more temperature rangevalues), the number of possible current % T values can be increased ordecreased (e.g., there could be eight possible optical states such as 5%T, 15% T, 25% T, 35% T, 45% T, 55% T, 65% T, and 75% T), the number ofpossible target % T values can be increased or decreased (e.g., to matchthe possible current % T states), among other suitable modifications.Additionally, the voltage profiles associated with each element of thematrix may have more than four profile portions or zones (e.g. S1-S8)with associated parameters. In some embodiments, for example, 8 zonesare permitted to be specified for each voltage profile, 12 voltageprofiles are permitted to be specified for the current ambienttemperature range, and 3 sets of 12 profiles are permitted to bespecified for the 3 temperature ranges specified. That combines to 288parameters for the voltage profile alone. Additional information alsocan be stored within memory device 292.

Additionally, in some embodiments in which a single window controller114 controls and drives two or more IGUs 102, each IGU 102 can stillinclude its own memory device 292. In such embodiments, each memorydevice 292 transmits its drive parameters to the single windowcontroller 114 and window controller 114, and particularlymicrocontroller 274, uses the drive parameters for the IGU having thesmallest size (and hence the lowest power requirements) to calculateV_(COMMAND) as an added safety to prevent damage. For example, windowcontroller 114 can include logic to identify the IGU size (e.g., length,width, thickness, surface area, etc.) or the IGU 102 can store sizeinformation within memory that can then be read by controller 114, e.g.,by microcontroller 274. In some embodiments, the microcontroller cancompare the drive parameters for two coupled IGUs 102, determine thatincompatible IGUs have been connected based on the compared driveparameters, and send an alarm to the BMS 110 or network controller 112.In some embodiments, the microcontroller 274 can use the driveparameters of the parallel-connected IGUs 102 to determine a safemaximum current drive for the aggregate group to further prevent damageto the IGUs.

Additionally, in some embodiments, each window controller 114 also canbe configured to compensate for transmission losses such as, forexample, voltage drops across bus bars 242 or 244 or down othertransmission lines in between PWM 276 and bus bars 242 and 244. Forexample, because PWM 276 (or some other component of window controller114 or IGU 102) can be configured to provide current feedback (e.g.,I_(FB)), microcontroller 274 (or some other logic component of windowcontroller 114) can be configured to calculate the voltage drop causedby transmission losses. For example, resistor R_(T) in FIG. 4 models thetransmission line resistance while resistor R_(S) in FIG. 4 models aseries resistance. R_(T) and R_(S) are inherent to the transmission lineor other system components. As current is supplied from the windowcontroller 114 it passes through R_(T), through IGU 102, and throughR_(S), before returning to the window controller 114 closing the loop.Because the current through R_(T), IGU 102, and R_(S) is known—by usingI_(FB) to set a fixed current output of the PWM 276 (e.g. 1 Ampere)—andbecause the differential amplifier 422 can be used to effectivelymeasure the voltage drop across R_(S), the values of R_(S) and R_(T) canbe calculated. For all intents and purposes, R_(T) can be approximatedby R_(S). Now, during normal operation of the device 220, because thecurrent demand through the IGU 102 is not constant, knowing theeffective resistance of the combination Rs+Rt allows for dynamicallyadjusting the voltage output from the window controller 114 so thedeveloped voltage V_(ACTUAL) at the terminals of the IGU 102 can becalculated as V_(ACTUAL)=V_(TARGET)+I_(ACTUAL)*(R_(S)+R_(T)) orV_(ACTUAL)=V_(TARGET)+2V(R_(S)), where V(R_(S)) is the voltage dropacross R_(S).

In one or more aspects, one or more of the functions described may beimplemented in hardware, digital electronic circuitry, analog electroniccircuitry, computer software, firmware, including the structuresdisclosed in this specification and their structural equivalentsthereof, or in any combination thereof Certain embodiments of thesubject matter described in this specification also can be implementedas one or more computer programs, i.e., one or more modules of computerprogram instructions, encoded on a computer storage media for executionby, or to control the operation of, data processing apparatus.

Various modifications to the embodiments described in this disclosuremay be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other implementationswithout departing from the spirit or scope of this disclosure. Thus, theclaims are not intended to be limited to the implementations shownherein, but are to be accorded the widest scope consistent with thisdisclosure, the principles and the novel features disclosed herein.Additionally, a person having ordinary skill in the art will readilyappreciate, the terms “upper” and “lower” are sometimes used for ease ofdescribing the figures, and indicate relative positions corresponding tothe orientation of the figure on a properly oriented page, and may notreflect the proper orientation of the devices as implemented.Additionally, as used herein, “or” may imply “and” as well as “or;” thatis, “or” does not necessarily preclude “and,” unless explicitly statedor implicitly implied.

Certain features that are described in this specification in the contextof separate embodiments also can be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation also can be implemented inmultiple implementations separately or in any suitable subcombination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this does not necessarily mean that the operations are requiredto be performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flow diagram. However, other operations thatare not depicted can be incorporated in the example processes that areschematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the implementations describedabove should not be understood as requiring such separation in allimplementations, and it should be understood that the described programcomponents and systems can generally be integrated together in a singlesoftware product or packaged into multiple software products.Additionally, other implementations are within the scope of thefollowing claims. In some cases, the actions recited in the claims canbe performed in a different order and still achieve desirable results.

What is claimed is:
 1. A window controller comprising: a command-voltagegenerator configured to generate a command voltage signal; apulse-width-modulated-signal generator configured to generate apulse-width-modulated signal based on the command voltage signal, thepulse-width-modulated signal configured to drive an optically-switchabledevice on a substantially transparent substrate, wherein: thepulse-width-modulated signal comprises a first power component having afirst duty cycle and a second power component having a second dutycycle; the first power component is configured to deliver a first pulseduring each active portion of the first duty cycle; the second powercomponent is configured to deliver a second pulse during each activeportion of the second duty cycle; and during operation, the first pulsesare applied to a first conductive electrode layer of theoptically-switchable device and the second pulses are applied to asecond conductive electrode layer of the optically-switchable device;wherein the relative durations of the active portions of the first andsecond duty cycles and the relative durations of the first and secondpulses are adjusted to result in a change in an effective DC voltageapplied across the optically-switchable device.
 2. The window controllerof claim 1, wherein the substantially transparent substrate isconfigured in an IGU.
 3. The window controller of claim 2, wherein thewindow controller is located at least partially within a seal of theIGU.
 4. The window controller of claim 2, wherein theoptically-switchable device is an electrochromic device formed on asurface of the substantially transparent substrate and adjacent aninterior volume of the IGU.
 5. The window controller of claim 4, whereinthe electrochromic device is entirely comprised of inorganic solid-statematerials.
 6. The window controller of claim 1, wherein: the first dutycycle has a first time period and a first voltage magnitude; the secondduty cycle has a second time period and a second voltage magnitude; thefirst time period equals the second time period; and the first voltagemagnitude equals the second voltage magnitude.
 7. The window controllerof claim 6, further comprising first and second inductors that couplethe first and second power components to the optically-switchabledevice, wherein the voltage applied across the optically-switchabledevice resulting from the applied first and second power components iseffectively a DC voltage.
 8. The window controller of claim 7, wherein:the active portion of the first duty cycle comprises a first fraction ofthe first time period; and the active portion of the second duty cyclecomprises a second fraction of the second time period.
 9. The windowcontroller of claim 8, wherein: the magnitude of the voltage applied toa first conductive layer of the optically-switchable device issubstantially proportional to the product of the first fraction and thefirst voltage magnitude; the magnitude of the voltage applied to asecond conductive layer of the optically-switchable device issubstantially proportional to the product of the second fraction and thesecond voltage magnitude; and the effective DC voltage applied acrossthe optically-switchable device is substantially equal to the differencebetween the magnitude of the voltage applied to the first conductivelayer and the magnitude of the voltage applied to the second conductivelayer.
 10. The window controller of claim 1, wherein the command-voltagegenerator includes a microcontroller configured to generate the commandvoltage signal.
 11. The window controller of claim 10, wherein themicrocontroller generates the command voltage signal based at least inpart on a voltage feedback signal that is itself based on an effectiveDC voltage applied across the optically-switchable device.
 12. Thewindow controller of claim 10, wherein the microcontroller generates thecommand voltage signal based at least in part on a current feedbacksignal that is itself based on a detected current transmitted throughthe optically-switchable device.
 13. The window controller of claim 10,further comprising a memory device configured to store one or more driveparameters.
 14. The window controller of claim 13, wherein the driveparameters include one or more of a current outside temperature, acurrent inside temperature, a current transmissivity value of theelectrochromic device, a target transmissivity value of theelectrochromic device, and a transition rate.
 15. The window controllerof claim 14, wherein the microcontroller is further configured to modifythe command voltage signal based on one or more other input, feedback,or control signals.
 16. The window controller of claim 15, wherein themicrocontroller modifies the command voltage signal based at least inpart on a voltage feedback signal that is itself based on a detectedactual level of the effective DC voltage applied across theoptically-switchable device.
 17. The window controller of claim 15,wherein the microcontroller modifies the command voltage signal based atleast in part on a current feedback signal that is itself based on adetected current transmitted through the optically-switchable device.18. The window controller of claim 15, wherein the window controllerfurther comprises one or more communication interfaces.
 19. The windowcontroller of claim 18, wherein: the window controller is configured tocommunicate with a network controller; the network controller isconfigured to communicate and control a plurality of window controllers;and the microcontroller is configured to modify the command voltagesignal based on input from the network controller.
 20. The windowcontroller of claim 19, wherein: the window controller or networkcontroller is configured to communicate with a building managementsystem; and the microcontroller is configured to modify the commandvoltage signal based on input from the building management system. 21.The window controller of claim 19, wherein: the window controller ornetwork controller is configured to communicate with one or morelighting systems, heating systems, cooling systems, ventilation systems,power systems, and/or security systems; and the microcontroller isconfigured to modify the command voltage signal based on input from theone or more lighting systems, heating systems, cooling systems,ventilation systems, power systems, and/or security systems.
 22. Thewindow controller of claim 19, wherein: the window controller isconfigured to communicate with one or more photodetectors; and themicrocontroller is configured to modify the command voltage signal basedon input from the one or more photodetectors.
 23. The window controllerof claim 19, wherein: the window controller is configured to communicatewith one or more temperature sensors; and the microcontroller isconfigured to modify the command voltage signal based on input from theone or more temperature sensors.
 24. The window controller of claim 19,wherein: the window controller or network controller is configured tocommunicate with one or more manual user-input devices; and themicrocontroller is configured to modify the command voltage signal basedon input from one or more of the manual user-input devices.
 25. A systemcomprising: a plurality of windows, each window comprising anoptically-switchable device on a substantially transparent substrate; anetwork controller configured to control a plurality of windowcontrollers; a plurality of window controllers, each window controllercomprising: a command-voltage generator configured to generate a commandvoltage signal; and a pulse-width-modulated-signal generator configuredto generate a pulse-width-modulated signal based on the command voltagesignal, the command voltage signal being based at least in part and atleast at certain times on an input received from the network controller,the pulse-width-modulated signal configured to drive a respective one ormore of the optically-switchable devices, one or more communicationinterfaces that enable the window controller to communicate with thenetwork controller; wherein: the pulse-width-modulated signal comprisesa first power component having a first duty cycle and a second powercomponent having a second duty cycle; the first power component isconfigured to deliver a first pulse during each active portion of thefirst duty cycle; the second power component is configured to deliver asecond pulse during each active portion of the second duty cycle; andduring operation, the first pulses are applied to a first conductiveelectrode layer of the optically-switchable device and the second pulsesare applied to a second conductive electrode layer of theoptically-switchable device; wherein the relative durations of theactive portions of the first and second duty cycles and the relativedurations of the first and second pulses are adjusted to result in achange in an effective DC voltage applied across theoptically-switchable device.
 26. The system of claim 25, wherein eachsubstantially transparent substrate is configured in an IGU.
 27. Thesystem of claim 26, wherein one or more of the window controllers arelocated at least partially within a seal of a respective IGU.
 28. Thesystem of claim 26, wherein the optically-switchable device is anelectrochromic device formed on a surface of the substantiallytransparent substrate and adjacent an interior volume of the IGU. 29.The system of claim 25, wherein, for each window controller: the firstduty cycle has a first time period and a first voltage magnitude; thesecond duty cycle has a second time period and a second voltagemagnitude; the first time period equals the second time period; and thefirst voltage magnitude equals the second voltage magnitude.
 30. Thesystem of claim 29, wherein each window controller further comprisesfirst and second inductors that couple the first and second powercomponents to the optically-switchable device, wherein the voltageapplied across the optically-switchable device resulting from theapplied first and second power components is effectively a DC voltage.31. The system of claim 30, wherein: the active portion of the firstduty cycle comprises a first fraction of the first time period; and theactive portion of the second duty cycle comprises a second fraction ofthe second time period.
 32. The system of claim 31, wherein: themagnitude of the voltage applied to a first conductive layer of theoptically-switchable device is substantially proportional to the productof the first fraction and the first voltage magnitude; the magnitude ofthe voltage applied to a second conductive layer of theoptically-switchable device is substantially proportional to the productof the second fraction and the second voltage magnitude; and theeffective DC voltage applied across the optically-switchable device issubstantially equal to the difference between the magnitude of thevoltage applied to the first conductive layer and the magnitude of thevoltage applied to the second conductive layer.
 33. The system of claim25, wherein the command-voltage generator of each window controllerincludes a microcontroller configured to generate the command voltagesignal.
 34. The system of claim 33, wherein the microcontrollergenerates the respective command voltage signal based at least in parton a voltage feedback signal that is itself based on an effective DCvoltage applied across the respective optically-switchable device. 35.The system of claim 33, wherein the microcontroller generates therespective command voltage signal based at least in part on a currentfeedback signal that is itself based on a detected current transmittedthrough the respective optically-switchable device.
 36. The system ofclaim 33, wherein each window controller further comprises a memorydevice configured to store one or more drive parameters.
 37. The systemof claim 36, wherein the drive parameters include one or more of acurrent outside temperature, a current inside temperature, a currenttransmissivity value of the electrochromic device, a targettransmissivity value of the electrochromic device, and a transitionrate.
 38. The system of claim 37, wherein the microcontroller modifiesthe command voltage signal based at least in part on a voltage feedbacksignal that is itself based on a detected actual level of the effectiveDC voltage applied across the respective optically-switchable device.39. The system of claim 37, wherein the microcontroller modifies thecommand voltage signal based at least in part on a current feedbacksignal that is itself based on a detected current transmitted throughthe respective optically-switchable device.
 40. The system of claim 33,wherein: the network controller is configured to communicate with abuilding management system; and the microcontroller of each windowcontroller is configured to modify the command voltage signal based oninput from the building management system.
 41. The system of claim 33,wherein: the network controller is configured to communicate with one ormore lighting systems, heating systems, cooling systems, ventilationsystems, power systems, and/or security systems; and the microcontrollerof each window controller is configured to modify the command voltagesignal based on input from the one or more lighting systems, heatingsystems, cooling systems, ventilation systems, power systems, and/orsecurity systems.
 42. The system of claim 33, wherein: each windowcontroller is configured to communicate with one or more photodetectors;and the respective microcontroller is configured to modify the commandvoltage signal based on input from the one or more photodetectors. 43.The system of claim 33, wherein: each window controller is configured tocommunicate with one or more temperature sensors; and the respectivemicrocontroller is configured to modify the command voltage signal basedon input from the one or more temperature sensors.
 44. The system ofclaim 33, wherein: the network controller is configured to communicatewith one or more manual user-input devices; and the microcontroller ofeach window controller is configured to modify the command voltagesignal based on input from one or more of the manual user-input devices.